Hello- when I try to flatten my image, things like layer transparency, adjustment layers, and blending modes are lost. I need to make a flat image of a PSD to send out for printing. When I merge 2 at a time, or 1 with an empty layer below it, or all at once, it still doesn't look right.
Try putting a layer of white at the bottom and flatten all layers at once. The problem is with layer blending modes needing a lyer underneath to blend to, and if you do not have the item in your selection group that the layer is blending to you can get innacurate results.
If that does not work try saving to a phtoshop .pdf. Phothsop .pdfs are great. tehre are many setting, but they are all there such as converting founts to outlines, so you dont have to send the font to the printer. You can later open this .pdf in illustrator, adn will see how shapes and type stay vector quality with the correct settings and hwo all bitmapped layers get flattened to make the file smaller.